Spray burner for the thermal decomposition of sulphur-containing residues

ABSTRACT

The aim of the invention is to produce a spray burner, starting from a conventional spray burner, for the atomisation and combustion of sulphur-containing residues, comprising a residue nozzle, for the introduction of sulphur-containing residue, which is surrounded by an outer nozzle, for the introduction of an atomising agent, whereby said burner is suitable for a method in which oxygen can be introduced in the cracking oven as additional oxidising agent to increase the capacity and improve the economic efficiency without the above disadvantages and limitations and is also optimised for a variable throughput of residue for atomising. Said aim is achieved whereby the residue nozzle comprises a multiplicity of individual nozzles which may be switched on and off, connected to an input for the residue, an inlet for fuel is provided and the outer nozzle is connected to an inlet for an oxygen-enriched gas stream.

[0001] The present invention relates to an atomizing burner for theatomization and combustion of residues containing sulfur, comprising aresidue nozzle that feeds in the residue containing sulfur and that issurrounded by an outer nozzle that feeds in an atomizing medium.

[0002] Such atomizing burners are used in the treatment of liquidresidues containing sulfur. According to the state of the art, residuescontaining sulfur such as, for example, spent sulfuric acids (so-called“waste sulfuric acids”) or ammonia sulfate solutions, are treated bymeans of thermal cleavage in so-called cleaving installations. In thisprocess, the residues are fed into a heating zone of a reactor with arefractory lining, hereinafter referred to as a “cleaving oven”, saidheating zone being created by hot flue gases, where these residues arethermally cleaved under formation of sulfur dioxide. The heating zone iscreated by burning a fuel with an oxidant that contains oxygen. Theprocess gases containing sulfur dioxide are further processed accordingto the state of the art into sulfuric acid, fuming sulfuric acid orsulfur dioxide.

[0003] Two different types of reactors are commonly used, which differprimarily in terms of the process gas flow, namely, cleaving ovens witha vertical or with a horizontal flow.

[0004] In the case of cleaving ovens with a vertical flow, the burnersfor generating the hot flue gases are flanged directly onto the ovenwall radially or tangentially in one or more planes. The flame firstdevelops in the cleaving oven, whereby CO and soot might form as aresult of incomplete combustion, and there is a risk that the sulfuricacid produced could acquire a brown coloration. Therefore, the moremodern cleaving installations are equipped with upstream combustionchambers, called combustors, rather than with the directly flanged-onburners. Combustors generate a hot, fully reacted flue gas at atemperature of about 2000° C. [3632° F.].

[0005] With the horizontally arranged cleaving oven, usually one or moreburners or combustors are flanged directly onto the end wall. The flameor the flue gas exit horizontally.

[0006] Examples of possible fuels are combustible gases and liquidfuels, preferably with a high sulfur content, such as, for example, fueloil. If there is a need to increase the sulfuric acid production, liquidsulfur is also added as the fuel, and it burns directly in the cleavingoven to form sulfur dioxide. The oxidation medium normally used is air,which is either added to the burner box at the ambient temperature orelse recuperatively heated.

[0007] All cleavage methods have in common the requisite very highcleavage temperature of 900° C. to 1200° C. [1652° F. to 2192° F.] atwhich the residues containing sulfur are converted into sulfur dioxide,water vapor, oxygen and optionally nitrogen and carbon dioxide. Thestrong endothermic cleavage reaction takes place in the cleaving ovensdescribed above, requiring large amounts of energy in the form ofcombustible gas or oil. Thus, for example, theoretically, about 1770 KWhof energy per ton of waste acid are needed for the cleavage of a70%-solution of waste sulfuric acid, consisting of 70% sulfuric acid and30% water.

[0008] When air is used as the oxidant, the inert nitrogen fraction alsohas to be heated to the cleavage temperature of about 1000° C. [1832°F.], thus additionally raising the energy consumption and reducing thesulfur dioxide concentration as well as increasing the process gasvolume.

[0009] In principle, the specific disposal costs per ton of waste acidcan be reduced by increasing the sulfur dioxide concentration in theprocess gas.

[0010] Higher sulfur dioxide concentrations can be achieved either byconcentrating the residues containing sulfur in a separate installationor by reducing the inert nitrogen fraction in the combustion air, whichis normally achieved by using oxygen as the oxidation medium.

[0011] In order to mix oxygen with the fuels in the cleaving oven, sofar, the following methods have proven their worth in actual practice:

[0012] enrichment of the combustion air with oxygen,

[0013] injection of oxygen into the air flame,

[0014] use of a fuel/oxygen burner.

[0015] As a result of the oxygen enrichment and/or the oxygen injection,the flame temperature rises, which can cause damage to the burnersand/or to the refractory lining.

[0016] During the oxygen enrichment as well as during the oxygeninjection, the temperature of the flame is raised, thus promoting thethermal formation of nitrogen oxide, which is fundamentallydisadvantageous for the cleaving process.

[0017] When a fuel/oxygen burner is used, fuels such as oil orcombustible gas are burned by means of a suitable burner, while beingmixed externally with oxygen. The oxygen burners can additionally beintegrated into the reactor so as to improve the performance of anexisting cleaving oven, or else to replace air burners. The very highflame temperatures of up to 2900° C. [5252° F.] give rise to the sameproblems as with the previously mentioned methods. Moreover,water-cooled oxygen burners are maintenance-intensive since corrosiondamage can occur on the cooled surfaces due to the condensation ofsulfuric acid.

[0018] Owing to these drawbacks, the use of oxygen to improve theperformance of cleaving installations used for regenerating residuescontaining sulfur has only been possible to a limited extent. Thus, forexample, cleaving ovens that were equipped with combustors could not beoperated with oxygen until now because the oxygen enrichment as well asthe oxygen injection cause the flame temperature to rise so that therefractory lining of the combustor, which is already being operated atits upper temperature limit, melts and moreover, due to the increasedformation of nitrogen oxide, the quality of the produced sulfuric acidis greatly diminished due to elevated content of nitrosyl sulfuric acid.

[0019] The acid is fed into the cleaving oven by means of pressureatomizers, compressed-air atomizers or rotary atomizers that are made ofacid-proof materials.

[0020] All types of atomizers have in common the atomizing nozzlepositioned centrally in the atomizer through which the entire amount ofresidue containing sulfur passes.

[0021] It is known that the degree of thermal cleavage of residuescontaining sulfur is inversely proportional to the size of the atomizeddroplets in the cleaving oven. As a matter of principle, a higher degreeof cleavage is achieved with small droplets of liquid.

[0022] When it comes to high-pressure atomizers and injector atomizerssuch as, for example, a compressed-air atomizer, the size of theatomized liquid droplets is proportional to the inner diameter of theatomizing nozzle and to the atomizing pressure. Therefore, atomizingnozzles are optimized for a prescribed pressure and throughput rate.Consequently, atomizing nozzles that were dimensioned for the maximumthroughput of waste acid no longer function optimally under partial loadconditions.

[0023] Therefore, the present invention is based on the objective ofproviding an atomizing burner that can be used, on the one hand, for aprocess in which oxygen can be introduced into the cleavage oven withoutthe above-mentioned drawbacks and limitations as an additional oxidationmedium in order to enhance the performance and improve thecost-effectiveness and that, on the other hand, is optimized for avariable throughput rate of the residue that is to be atomized.

[0024] Using the above-mentioned atomizing burner, this objective isachieved according to the invention in that the residue nozzle comprisesa plurality of individual nozzles that can be turned on or off and thatare connected to an inlet for the residue, in that a feed inlet isprovided for the fuel and in that the outer nozzle is connected to aninlet for an oxygen-rich gas stream.

[0025] Thanks to the plurality of individual nozzles in the atomizingburner according to the invention, instead of the central atomizedliquid cone known from the state of the art, several individual atomizedliquid cones are formed with the residue that is to be treated.

[0026] The individual nozzles are designed so that they can be turned onor off, as a result of which the throughput of residue through theindividual nozzles can be adapted to the requirements at hand. In thismanner, it is especially possible to ensure that, when the throughput isincreased or decreased, a droplet size ascertained to be optimal can bemaintained for at least some of the individual nozzles in that thethroughput through one or more of the individual nozzles is turned on oroff.

[0027] Moreover, the atomizing burner according to the invention has afeed inlet for fuel and for an oxygen-rich gas. The burning of the fuelwith the oxygen-rich gas supplies cleaving energy in the area of theatomizing burner—and thus in a pre-reaction zone that is separate fromthe actual reaction zone. In this pre-reaction zone, the residuecontaining sulfur is partially cleaved and only then is it fed into thereaction zone consisting of the hot flue gases at a higher temperature,where the residue is then completely cleaved. Since the pre-reactionzone is thus separate from the actual reaction zone, the additionalenergy needed in the pre-reaction zone to enhance the performance can besupplied without this causing an increase in the flame temperature inthe actual reaction zone and hence without exceeding the temperaturelimits in this area or else increasing the formation of nitrogen oxide.

[0028] Due to the joint introduction of the residue and of the fuel intothe pre-reaction zone and the partial cleavage of the residue, thethermal cleavage of the residue can be carried out in the actualreaction zone at low reaction temperatures, which translates into a lowformation of nitrogen oxide at high reaction rates in the overallprocess. The reaction products from the pre-reaction zone that had notyet been completely cleaved are transferred to the actual reaction zonehaving a higher temperature, where the complete cleavage and combustionof the reaction products takes place without the additional formation ofnitrogen oxide.

[0029] The oxygen-rich gas stream consists of pure oxygen or of anoxygen-air mixture with an oxygen concentration between 25 vol.-% and100 vol.-%. It surrounds the droplet streams of residue and fuel asthese are formed and it serves as the oxidant and, at the same time, asthe secondary atomizing medium.

[0030] An especially precise and variable adaptation to the throughputrate is achieved with an atomizing burner in which the individualnozzles are designed so that they can be turned on or off. For thispurpose, for example, each individual nozzle can be associated with avalve.

[0031] In particular, an atomizing burner in which the number ofindividual nozzles is at least 2 and at the most 9 has proven its worth.As the number of individual nozzles increases, the optimization of thedroplet size to the momentary throughput becomes more precise. The upperlimit indicated results from the increasing demands associated with anincreasing number of individual nozzles. Normally, a symmetricalarrangement of the individual nozzles—in the direction of the lengthwiseaxis of the atomizing burner—is preferred since this facilitates theproduction of the atomizing burner as well as the homogeneous mixing andreproducible distribution of the residue, of the fuel and of the oxygenin the pre-reaction zone.

[0032] In a preferred embodiment of the atomizing burner, there is acentral inner nozzle that feeds in the fuel and individual nozzlesarranged around the central inner nozzle. In order to generate thecleaving energy needed in the pre-reaction zone, liquid and/or gaseousfuel is injected through the central inner nozzle of the atomizingburner into the droplet streams consisting of residues containing sulfurthat is coming out of the individual nozzles. The fuel penetrates thedroplet streams and reacts with the oxygen-rich gas, thus creating theabove-mentioned pre-reaction zone. Aside from the fuel, other componentscan also be introduced into the pre-reaction zone via the inner nozzle,especially a mixture of fuel and residue, whereby in that case, theinner nozzle is connected to an inlet for the residue. Consequently, theinner nozzle should also be considered to be an individual nozzle as setforth in this invention.

[0033] As an alternative or supplement to this, the cleaving energyneeded in the pre-reaction zone is generated by mixing liquid fuel withthe residue containing sulfur outside of the atomizing burner and byinjecting the residue-fuel mixture into the reactor through theindividual nozzles. Therefore, advantageously, the individual nozzlesare connected to a mixing device that makes the mixture consisting ofresidue and fuel.

[0034] The atomizing burner according to the invention makes it possibleto atomize the residue while feeding in an oxygen-rich gas streamthrough the outer nozzle. In order to protect the individual nozzles orthe inner nozzle against chemical attack by the oxygen-rich gas stream,it has proven to be advantageous to provide an inert gas nozzle betweenthe individual nozzles and the outer nozzle. By feeding a suitable inertgas through the inert gas nozzle, the individual nozzles and—ifpresent—the inner nozzle are protected against the oxygen-rich gasstream. Consequently, it is possible to make the individual nozzlesand/or the inner nozzle out of a material that would otherwise besusceptible to corrosion under ambient conditions.

[0035] Preferably, the individual nozzles and—if present—the innernozzle are made of zirconium. Zirconium stands out for its high acidresistance and durability, but at high temperatures (for example, at1000° C. [1832° F.]), due to its affinity, it oxidizes readily or mighteven be ignited in pure oxygen, which is prevented by the medium fed inthrough the inert gas nozzle.

[0036] An especially simple embodiment of the atomizing burner is one inwhich the outer nozzle is configured as an annular gap that coaxiallysurrounds the inert gas nozzle.

[0037] In an alternative and likewise preferred embodiment of theatomizing burner, the outer nozzle is configured as an annular gap inwhich a plurality of tubular nozzles are distributed along the outerperimeter of the inert gas nozzle. With this embodiment of the atomizingburner, a first gas can be fed in through the annular gap and a secondgas through the tubular nozzles. For example, the first gas can bepreheated air and the second gas can be an oxygen-rich gas stream as setforth in this invention, having an oxygen content of preferably at least80 vol.-%. dr

[0038] Below, the invention will be explained in greater depth withreference to embodiments and a drawing. The drawing shows the followingin detail:

[0039]FIG. 1—the atomizing burner according to the invention in a firstembodiment, and

[0040]FIG. 2—the atomizing burner according to FIG. 1 in a top view ofthe opening of the atomizing nozzle.

[0041] The atomizing burner shown in FIG. 1 has a central inner nozzle 1around which a bundle of a total of four individual nozzles 3 areuniformly distributed. The inner nozzle 1 and the individual nozzles 3are coaxially surrounded by an ring-shaped gas separation nozzle 4 andby another ring-shaped outer nozzle 5. The inner nozzle 1 has an inlet 6that feeds in fuel. The individual nozzles 3 are connected to an inlet 7via which the individual nozzles 3 are supplied either with fuelcontaining sulfur or else with a mixture of fuel and residue containingsulfur.

[0042] In an alternative embodiment of the atomizing burner, the innernozzle 1 is also connected to an inlet (not shown in FIG. 1) that feedsin a mixture of fuel and residue containing sulfur.

[0043] Thus, via the inlets 6 and 7, either a mixture of fuel andresidue containing sulfur is fed to the atomizing burner or else theresidue is fed in via the inlet 7 separately from the fuel (inlet 6). Inthe latter case, either liquid fuel (such as light or heavy oil, wasteoil or solvent) or else a combustion gas (such as natural gas, propane,butane or other combustible gases) is fed in through the inlet 6 whilethe residue containing sulfur is fed in through the inlet 7.

[0044] The gas separation nozzle 4 is provided with an air inlet and theouter nozzle 5 is provided with an inlet 9 for an oxygen-air mixturewhose oxygen content can be varied between 20.6 vol.-% and 100 vol.-%and that can be heated to a temperature of up to 600° C. [1112° F.].

[0045] Inside the ring-shaped outer nozzle 5, there is a plurality oftubular nozzles 10 (in the embodiment there are eight tubular nozzles10), which have a circular cross section. The tubular nozzles 10 aredistributed evenly around the gas separation nozzle 4. They consist oftubes made of austenitic material whose upper end facing away from thenozzle opening 11 is connected to an oxygen inlet 12 that feeds intechnically pure oxygen.

[0046] Through this arrangement of the individual nozzles, the oxygen isseparated from the preheated oxygen-air mixture until the nozzle opening11. In this manner, any desired amount of oxygen or air can be safelyfed into the oven.

[0047] The top view of the opening of the atomizing nozzle according toFIG. 2 shows the coaxial arrangement of the individual tubes (13; 14;15) and of the nozzles (1, 3, 5) as well as the arrangement of thecircular tubular nozzles 10 around the gas separation nozzle 4 and ofthe individual nozzles 3 around the inner nozzle 1 in the atomizingburner according to FIG. 1.

[0048] The individual nozzles 3 and the inner nozzle 1 are formed by atube bundle made of zirconium. The other walls of the nozzles (4; 5)consist of a heat-proof, sulfur-resistant, high-alloy stainless steel inthe form of two coaxial tubes (14; 15).

[0049] The advantages of the atomizing burner according to the inventionin comparison to the atomizing burners according to the state of the artare compiled below in bulleted form:

[0050] Optimization of the droplet size and of the atomizing pressure inthe waste acid in the case of varying amounts of waste acid byindependently turning on or off individual atomizing nozzles

[0051] Long service life of the individual atomizing nozzles due to theuse of zirconium as the material in view of the inert gas introducedthrough the gas separation nozzle, even when pure oxygen is used as theatomizing and oxidation medium

[0052] Performance increase due to the use of an oxygen-rich gas as theoxidation agent with the formation of a pre-reaction zone having a lowertemperature into which oxygen, fuel and residue are introduced together,where the residue is partially cleaved and only then fed into the actualreaction zone having a higher temperature.

1. An atomizing burner for the atomization and combustion of residuescontaining sulfur, comprising a residue nozzle that feeds in the residuecontaining sulfur that is surrounded by an outer nozzle that feeds in anatomizing medium, characterized in that the residue nozzle comprises aplurality of individual nozzles (3) that can be turned on or off andthat are connected to an inlet (7) for the residue, in that a feed inlet(9) is provided for fuel and in that the outer nozzle (5) is connectedto an inlet (9) for an oxygen-rich gas stream.
 2. The atomizing burneraccording to claim 1, characterized in that the individual nozzles (3)are designed so that they can be turned on or off individually.
 3. Theatomizing burner according to claim 1 or 2, characterized in that thenumber of individual nozzles (3) is at least 2 and at the most
 9. 4. Theatomizing burner according to one of the preceding claims, characterizedin that there is a central inner nozzle (1) that feeds in the fuel andindividual nozzles (3) are arranged around the central inner nozzle (3).5. The atomizing burner according to one of claims 1 to 4, characterizedin that the individual nozzles (3) are connected to a mixing device thatmakes the mixture consisting of residue and fuel.
 6. The atomizingburner according to one of the preceding claims, characterized in thatthere is an inert gas nozzle (4) between the individual nozzles (3) andthe outer nozzle (5).
 7. The atomizing burner according to one of thepreceding claims, characterized in that the individual nozzles (3) aremade of zirconium.
 8. The atomizing burner according to one of thepreceding claims, characterized in that the outer nozzle (5) isconfigured as an annular gap that coaxially surrounds the inert gasnozzle (4).
 9. The atomizing burner according to one of claims 1 to 11,characterized in that the outer nozzle (5) comprises an annular gap inwhich a plurality of tubular nozzles (10) are distributed along theouter perimeter of the inert gas nozzle.